Gallium nitride is being widely investigated for microelectronic devices including but not limited to transistors, field emitters and optoelectronic devices. It will be understood that, as used herein, gallium nitride also includes alloys of gallium nitride such as aluminum gallium nitride, indium gallium nitride and aluminum indium gallium nitride.
A major problem in fabricating gallium nitride-based microelectronic devices is the fabrication of gallium nitride semiconductor layers having low defect densities. It is known that one contributor to defect density is the substrate on which the gallium nitride layer is grown. Accordingly, although gallium nitride layers have been grown on sapphire substrates, it is known to reduce defect density by growing gallium nitride layers on aluminum nitride buffer layers which are themselves formed on silicon carbide substrates. Notwithstanding these advances, continued reduction in defect density is desirable.
It is also known to fabricate gallium nitride structures through openings in a mask. For example, in fabricating field emitter arrays, it is known to selectively grow gallium nitride on stripe or circular patterned substrates. See, for example, the publications by Nam et al. entitled "Selective Growth of GaN and Al.sub.0.2 Ga.sub.0.8 N on GaN/AlN/6H--SiC(0001) Multilayer Substrates Via Organometallic Vapor Phase Epitaxy", Proceedings of the Materials Research Society, December 1996, and "Growth of GaN and Al.sub.0.2 Ga.sub.0.8 N on Patterened Substrates via Organometallic Vapor Phase Epitaxy", Japanese Journal of Applied Physics., Vol. 36, Part 2, No. 5A, May 1997, pp. L532-L535. As disclosed in these publications, undesired ridge growth or lateral overgrowth may occur under certain conditions.